Biofouling is a known phenomenon and has been investigated for a long time, which consists in the sedimentation of different species of organisms (from single proteins to microorganisms like bacteria and protozoans, to complex macroorganisms like serpulids and bryozoans) on artificial substrates that are immersed in water environments. Typically, the biofouling phenomenon takes place on substrates placed in water environments, with the consequential technological alteration of the objects: already after an hour of immersion, an initial film consisting of bacteria and other microorganisms begins to form on the hull of a boat; biofouling has, over time, negative repercussions in various nautical fields, like commercial boating, pleasure boating, and competitive boating. The organisms that constitute the biofouling, in fact, lead to deterioration, discoloring and corrosion of the objects subject to biofouling, with the subsequent loss of performance, and increase in the fuel consumption. To avoid the problems caused by the aesthetic and structural decline of the objects placed in direct contact with the water environment, repeated treatments and laying ups on the abovementioned objects are necessary.
The most efficient system to fight against biofouling is to apply antifouling paint directly on the products subject to biofouling. The first formulations of these paints, going back to the 60's, are based on products that are self-smoothing with an organostannic polymeric matrix. The objects treated with these formulations slide well in the water, at the expense of having, however, a high environmental impact. In fact, these paints typically contain tributyltin (TBT); this chemical compound is highly toxic: the TBT-based biocides accumulate in the sediments and in the food chains, which irreversibly modify the various ecosystems. The introduction of some community laws tried to hold this environmental problem in check, by imposing the use of other organometallic and organic biocide based paints.
Currently numerous patents exist regarding eco-compatible antifouling paints based on other types of biocide; however, all these products have intrinsic and evident deficiencies in performance and/or durability. For example, the self-smoothing (or hydro-erodible) paints and the “hybrid” paints, or rather the self-smoothing/releasing antifouling chemicals that are not specifically biocides, are lacking in performance because the antifouling coating has a short duration, and are not easily predictable/controllable as a function of the variability of the environmental conditions of the waters and the work regime.
The paints containing organic biocides that don't damage (or claimed as to be not damaging) the water environment, not only have a progressive loss in coating efficiency and are not easily controllable like for the self-smoothing paints, but also show important hygienic and environmental implications; in fact, these products have eco-effects that have not been sufficiently studied and/or known over long term, and potential health risks for the operators during the step of manipulating the product.
The chemically inert or bio-inert paints with a low surface tension are instead perfectly eco-compatible, but do not adhere well to the substrates to which they are applied, and have a reduced mechanical resistance and resistance to abrasion.
Finally, the chemically inert and bio-inert paints with a very low surface tension with a diversified polymeric nature and partially fluorized, show good efficiency, but poor durability due to lacking cohesiveness and poor adhesiveness of the coating to the majority of substrates.
Currently, different types and brands of antifouling products can be found on the market, which are all based on a formulation of the film that is able to dissolve biologically active chemical compounds in water. The toxicity of these chemical compounds is able to inhibit fouling on the immersed structures, by efficiently repelling or killing settled organisms.
Substantially, there are three forms of biocide release:
1. release due to hydration;
2. release due to erosion;
3. release due to hydrolytic degradation of the matrix.
Depending on the type of boat and/or object that is immersed, its use, and the quality of the water in which it is allocated and/or in which it has its principal use, four types of biocide paints can be identified:
1. traditional paints with a soluble matrix, wherein the biocide release occurs due to the erosion of the bonding polymer;
2. paints with a partially soluble matrix (long-life), wherein the biocide release occurs due to the hydration and erosion of the film;
3. paints with a hard or insoluble matrix, wherein the biocide release occurs due to hydration;
4. self-smoothing or self-polishing paints, wherein the biocide release occurs due to the hydrolytic degradation of the matrix.
All of these paints contain biocides that are different from the tributyltin compounds, in which copper based compounds play an important role, but these are also intrinsically damaging to the environment, though less so than compared to TBT-based products. For this reason, it is highly probable that these biocides, which are commonly used today, will be banned or their use limited in the near future through community or world-wide laws.
For all of the reasons mentioned above, an eco-compatible method for preventing and controlling the formation of biofouling that occurs in water environments and which avoids the use of products which are dangerous to the environment (with the possibility of being against the current laws regarding biocides) is highly desirable.